The present invention relates to fiber optic modules, and more particularly, to a module for housing an array of optoelectronic devices and a method for coupling light between the devices and fibers contained within a conventional fiber optic ferrule.
Fiber optic technology is widely utilized in today""s telecommunication and data communication network. One important aspect of this technology is the interconnection of optical fibers to optoelectronic devices such as semiconductor lasers and photodetectors, wherein the optoelectronic devices either receive optical radiation from the optical fibers or the optoelectronic devices emit optical radiation into the fibers. A good optical interconnect between an optical fiber and an optoelectronic device preferably provides high coupling efficiency, ease of assembly, and low cost manufacturing.
Conventional single-mode fiber optic modules are pigtailed devices, in which the optoelectronic device to fiber connection is completely contained within the module. Most modules are also hermetically sealed and are serial links, in which one transmit and/or one receive channel are contained within the module. Pigtailing and hermetically sealing, however, result in relatively high costs and serial links require a large amount of board space per optical channel in switching boxes.
In the data communications market, there are also numerous multi-mode fiber optic modules available. The majority of these modules do not have pigtails and are not hermetically sealed, except for the optoelectronic device itself. Non-pigtailed, non-hermetically sealed modules are known as connectorized modules. These connectorized modules are generally smaller and less expensive. The multi-mode fibers are generally 50 or 62.5 microns in core diameter, and therefore provide for easy alignment of the fiber to the optoelectronic device. Conventional single-mode fibers are 9 microns in diameter and are therefore more difficult to align and present greater challenges in forming connectorized modules.
Optoelectronic device array modules are available in the data communications market, but to date are limited to 850 nm vertical cavity surface emitting laser (VCSEL) array modules. An array transmitter is desirable because it provides a very high number of optical channels per inch of board space in the switching box. Thus far, these array modules are limited to multi-mode applications and therefore are limited in transmission distance. It would be desirable to have an array of long wave single mode VCSELs that provides the benefits of increased density of optical channels for a given board space and increased transmission distance.
The output optical power of VCSELs sometimes fluctuates due to changing environment such as temperature variation, aging behavior of the VCSELs, or circuit property drift in the laser drive circuitry. In a conventional single or serial transmission link, a photodetector receives a proportional fraction of the laser light emitted from the laser, and delivers a feedback signal to the laser drive circuit to correct the laser output optical power fluctuation. However, this method may be inefficient for an optical interconnect system involving an array of VCSELs, because it would require a photodetector and a feedback circuit for each and every one of the VCSELs.
In an exemplary embodiment, the present invention provides a VCSEL array within an optical subassembly module with an alignment.a connectorized array of VCSELs with high coupling efficiency includes a photodetector capable of monitoring the representative optical output of the VCSELs.
In particular, the present invention provides a method and apparatus for coupling light from an array of optoelectronic devices to a corresponding array of fibers contained in a conventional fiber optic ferrule. The fibers may be single-mode or multi-mode optical fibers. The method includes fixing the conventional fiber optic ferrule to the optical subassembly (OSA) base upon which the array of optoelectronic devices will be affixed, aligning the array of optoelectronic devices to the corresponding array of fibers, then securing the array of optoelectronic devices to the OSA base. A connectorized, nonpigtailed module is produced.
In an exemplary embodiment, the module includes an optical subassembly module housing a linear array of 1300 nm VCSELs or photodetectors, spaced apart at a 250 micron pitch, which corresponds to the spacing of optical fibers in a conventional MT ferrule. The substrate subassembly includes a lower weldable surface and the OSA base is formed of a weldable metal. After the components are aligned by maneuvering the components relative to one another, the substrate assembly is affixed to the OSA base by epoxying or welding.
The array of optoelectronic devices is mounted on a substrate assembly that includes a photodetector. The array of optoelectronic devices is mounted on a material within the substrate assembly that is transparent to the emitted light or includes a notch or hole that allows light to pass through, in order to facilitate the integral placement of the monitor within the substrate assembly and beneath the material. The monitor may be a photodetector capable of monitoring the representative optical output of the VCSELs.